The present invention relates to a surface microscope utilizing tunnel current or field emission current produced when a probe is brought close to a sample, and in particular to a surface microscope suitable for measuring tunnel barrier (tunneling barrier height), by means of which it is possible to find an interface, at which physical properties change at the neighborhood of the surface of the sample, e.g. an interface between the p type semiconductivity and the n type semiconductivity region at the surface of a semiconductor body, by measuring the tunnel barrier at the surface of the sample.
Heretofore a method for measuring the tunnel barrier by measuring tunnel current or field emission current produced when a probe is brought close to a sample is discussed in Phys. Rev. Lett. 49, 1982, pp. 57-61.
By the prior art technique described above it is disclosed to measure indirectly the value of the square root of the tunnel barrier, using the following equation, to calculate it; EQU .phi..sup.1/2 =(ln J.sub.T)/.DELTA.S (1)
That is, .phi..sup.1/2 can be measured, based on the tunnel current density J.sub.T and variations .DELTA.S in the gap between the probe and the sample. Between them, .DELTA.S can be set by vibrating the probe. J.sub.T is obtained by dividing the intensity of the tunnel current by the current emission area. However the emission area is not known at all. Further, the current density J.sub.T is varied also by absolute variations of the gap. Even in the case where a scanning tunneling microscope (STM), which is a kind of surface microscope, is driven in the constant current mode, since erroneous current from about 10% to several tens % is produced, it gives rise to errors of the current density J.sub.T. Consequently, there is a problem that, in the prior art it is not possible at all to measure the tunnel barrier (.phi.), even if Eq. (1) is used.